What he said, of course in the sql command you should personalize your user and password
so to do so, log into your sql command line ( mysql -u root -p if you've set a sql password or mysql -u root if you haven't )
and then type the commands from the tutorial but personalize them...

so...

Code:

CREATE DATABASE roundcubemail;
GRANT ALL PRIVILEGES ON roundcubemail.* TO roundcubeuser@localhost IDENTIFIED BY 'password';

where...Rouncubeuser is the actual user like root or anyother one ( let's say we'll change it to roundcubetest )Password : is the actual password used to log into that database, so you should not leave password of course... you can and must change it, (lets say it would be 123456 )

the final code for sql would be ,

Code:

CREATE DATABASE roundcubemail;
GRANT ALL PRIVILEGES ON roundcubemail.* TO roundcubetest@localhost IDENTIFIED BY '123456';

afterwards in the config files also go to the step where it asks for info about you SQL server, there at the username input "roundcubeuser" ( in my example is roundcubetest )
password as well ( in my ex is 123456 ) and the server is of course localhost aka 127.0.0.1